CD-1 mice are a widely used, general-purpose laboratory mouse stock and a foundational model in biomedical research. This stock is utilized globally due to its robust health and predictable breeding performance in a laboratory setting. The prevalence of CD-1 mice stems from their unique genetic background, which provides an animal model that responds to treatments and conditions in a way relevant to broader human populations. This article explains the history of the CD-1 stock, the scientific logic behind its genetic makeup, and its primary research applications.
Origin and Classification of CD-1 Mice
The lineage of the CD-1 mouse stock traces back to the Swiss mouse stock, an albino population derived from nine mice in Lausanne, Switzerland, during the 1920s. These progenitors were imported into the United States in 1926 by Dr. Clara Lynch of the Rockefeller Institute. The stock was later maintained at the Institute for Cancer Research (ICR) in Philadelphia, leading to the nomenclature Ha/ICR.
The stock was transferred to Charles River Laboratories in 1959, which is where the “CD-1” designation originates, standing for Charles River Laboratories-Derived. CD-1 is technically an “outbred stock,” which is distinct from an “inbred strain,” such as the C57BL/6 mouse. An outbred stock is a closed population of genetically diverse animals bred to maintain maximum genetic variation. In contrast, an inbred strain consists of mice that are genetically identical to one another due to generations of brother-sister mating.
Genetic Variability and Its Scientific Purpose
The CD-1 stock is categorized as an outbred population, meaning its individuals are genetically variable and heterozygous at many genetic loci, similar to a general human population. This genetic diversity is the primary scientific reason for the stock’s widespread use. It allows researchers to study a range of individual responses to a given treatment or exposure, unlike an inbred strain where all individuals respond in a highly predictable and similar manner.
The genetic makeup of the CD-1 mouse closely mimics the variability found within human populations, making it useful for certain types of testing. For example, in reproductive toxicology studies, the CD-1 population shows a range of sensitivity to environmental toxins, reflecting what might be observed in a human population. This heterogeneity makes the CD-1 mouse a robust model for studies that require population-level responsiveness rather than a uniform, single-point result.
Genetic variability is maintained through specialized breeding systems, such as the International Genetic Standardization (IGS) system, to minimize inbreeding and prevent genetic drift. The polymorphic Major Histocompatibility Complex (MHC) in CD-1 mice includes six to eight Class I variants. This supports a more diverse immune response compared to the single haplotype found in an inbred mouse. This diverse immune profile makes them valuable for research involving vaccine development and general immunology studies.
Primary Research Applications
The CD-1 mouse’s genetic variability and robust nature make it an ideal model for large-scale safety and efficacy testing across the pharmaceutical industry. General toxicology and safety testing are primary applications, as the diverse genetic background helps researchers identify potential human health risks across a population. The stock is frequently used to evaluate the metabolic fate of new drugs, with studies showing that drug concentration changes in CD-1 mice can align closely with data observed in human clinical trials.
The stock is widely used for reproductive and developmental toxicology studies, often serving as the standard model for assessing the effects of compounds on fertility and embryo-fetal development. Their robust physiology and adaptability allow them to withstand the long-term studies required for evaluating the chronic consequences of toxin exposure.
CD-1 mice play a significant role in general efficacy screening, especially in early-stage drug development, where a resilient, all-purpose model is required for initial compound testing. The ability of the CD-1 mouse to model diverse responses is leveraged in certain areas of neuroscience, such as anxiety research. Their behavioral responses to certain antidepressants have shown similarities to human patients.
Key Behavioral and Physical Characteristics
CD-1 mice are known for their strong reproductive performance, which is a practical benefit for maintaining large, cost-effective research colonies. Females typically have a gestation period of 19 to 21 days and produce an average litter size of eight to twelve pups. Their high reproductive performance, characterized by large litter sizes and excellent maternal care, makes them practical for complex, high-throughput studies. Their overall robust health and strong immune function mean they are well-equipped to handle the rigors of long-term studies.
Physically, the CD-1 mice are an albino stock, meaning they have white fur and red eyes due to a lack of pigmentation. Adult males are generally larger than females, with males weighing between 35 and 40 grams and females between 25 and 35 grams. The CD-1 stock is generally described as docile and easy to handle, which simplifies laboratory procedures and reduces stress-related variability in experiments.
Male CD-1 mice can exhibit more aggressive behaviors and territorial marking compared to the widely used C57BL/6 inbred strain. This is a factor researchers must consider when designing social behavior studies. The ease of handling combined with their high adaptability makes the CD-1 mouse stock a reliable choice for researchers across many different scientific disciplines.